The present invention relates to the design and fabrication of integrated circuits. More specifically, the present invention pertains to the design and fabrication of integrated circuits used in printheads for ink-jet printers.
Ink-jet printer cartridges include printhead structures in which small droplets of ink are formed and ejected toward a printing medium. The printhead structures have orifice plates incorporating very small nozzles through which the ink droplets are ejected. Ejection of an ink droplet through a nozzle is accomplished by heating a volume of ink in an adjacent ink chamber. The expansion of the ink forces a droplet of ink through the nozzle, a process referred to as xe2x80x9cfiring.xe2x80x9d The ink in the chamber is typically heated with a resistive heating material aligned with the nozzle and chamber.
Prior Art FIG. 1 illustrates an exemplary ink-jet printer cartridge 12 used in a printer such as a thermal ink-jet printer. A printhead 20 with an orifice plate 33 is fit into the bottom of the cartridge 12. The printhead 20 includes nozzles 25 through which ink is ejected in a controlled pattern during printing. Depending on the resolution of the printer, an array of 600 or more nozzles may be used. A flexible circuit 24 is mounted to the exterior of the cartridge 12. Circuit contact pads 23 are for electrically coupling the cartridge 12 to a matching circuit in the printer.
Prior Art FIG. 2 is a cross-sectional view of a portion of printhead 20 comprising a substrate 10, a conductive layer 22, and a printhead structure 40. For simplicity of illustration, a single printhead structure 40 is shown; however, in actuality, many (e.g., 600) printhead structures are used.
Substrate 10 is typically a silicon wafer although other materials may be used. Substrate 10 may be separated from the conductive layer 22 by an insulation layer 14 (e.g., a dielectric). Insulation layer 14 may be omitted if substrate 10 possesses dielectric and heat transfer characteristics suitable for directly receiving conductive layer 22.
In general usage and as used herein, conductive layer 22 is a generic term that includes both metallic (e.g., aluminum) lines and complementary metal oxide semiconductor (CMOS) logic circuits. Conductive layer 22, under control of a microprocessor and associated drivers in the printer, selectively distributes electrical signals to each of the printhead structures 40 so that they fire in a controlled pattern to produce on the printable medium the desired characters and images.
Printhead structure 40 includes resistive heating material (resistor) 30 adjacent to a firing chamber 44, an ink barrier 38, and a nozzle 25 formed in orifice plate 33 and in fluid communication with firing chamber 44. Conductive layer 22 includes a bonding pad 27 to which a lead from flexible circuit 24 (FIG. 1) is attached. Flexible circuit 24 carries signals generated by the microprocessor and associated drivers in the printer to conductive layer 22 via bonding pad 27. These signals prescribe which of the printhead structures 40 are to fire, depending on the character or image to be generated. Conductive layer 22 selectively provides electrical signals to resistor 30, which in turn produces an amount of heat sufficient for vaporizing some of the ink in firing chamber 44, thereby forcing an ink droplet through nozzle 25.
A problem with printheads of the prior art is that care must be taken to ensure that the electrical connections from the printer and/or print cartridge to the printhead structure are not exposed to the ink ejected from the printhead structure. The ink droplets exist as a fine mist (aerosol) and, although directed to the printable medium, may float back onto printhead structure 40, conductive layer 22, and the connection between bonding pad 27 and flexible circuit 24 (FIG. 2). Therefore, the electrical connections and other components are generally coated with some type of protective material to shield them from the ink.
However, the ink is very corrosive and eventually may penetrate the protective coating and damage electrical connections in the bond 27 between conductive layer 22 and flexible circuit 24, in conductive layer 22, or elsewhere. Electrical connections to some of the printhead structures or emanating from any other source may consequently fail or degrade to the point where current sufficient for heating resistor 30 cannot be provided. As a result, some of the printhead structures may not fire when they are supposed to, thus reducing print quality. To address this problem, what is needed is a method and/or apparatus that can protect electrical connections in the printhead from the corrosive effects of ink.
Another problem with the prior art is that the routing of the electrical signals to the printhead structures 40 can consume valuable space in printhead 20. As the number of printhead structures 40 increases (e.g., to achieve higher print qualities), the routing of the signals to the resistors 30 consumes more of the surface area on substrate 10. In addition, the routing of signals becomes more complex with an increasing number of printhead structures 40.
These latter problems are also experienced in applications other than ink-jet printers that utilize packaged integrated circuits (e.g., a semiconductor or integrated circuit die coupled with one or more structures or logic devices and mounted on a substrate). Generally, contacts for electrical signals from external sources to a packaged integrated circuit are situated toward the edge of the package or substrate. External electrical signals are therefore routed to the edge of the package or substrate, then routed to the various devices or structures that are included in the package. As logic devices become more complex, the routing of electrical signals to the integrated circuit package and within the package becomes more difficult and consumes greater quantities of the limited space available.
Therefore, what is also needed is a method and/or apparatus that can reduce the difficulty of routing electrical signals to integrated circuits and integrated circuit packages and that can reduce the area consumed by such routing, not only in ink-jet printers but in other applications as well. The present invention provides a novel solution to the above needs.
The present invention provides both an apparatus that can protect electrical connections from the corrosive effects of ink in an ink-jet printer and a method of forming such an apparatus. In addition, the present invention provides an apparatus (and a method for forming an apparatus) that can reduce the difficulty of routing electrical signals and that can reduce the area consumed by such routing, not only in ink-jet printers but in other applications as well.
The present invention pertains to an apparatus incorporating multiple electrical interconnects extending through a substrate (e.g., a silicon wafer). The electrical interconnects convey electrical signals through the substrate to structures (devices) mounted on the front side of the substrate. Accordingly, it is not necessary to route electrical signals to or along the front surface of the substrate in order to convey the signals to the structures, thereby reducing the difficulty of routing electrical signals as well as reducing the area consumed by such routing.
In one embodiment, each structure is electrically coupled to multiple parallel electrical interconnects extending through the substrate such that the electrical signals are carried to the structure by redundant electrical paths. The use of redundant paths can improve reliability because if an electrical interconnect should fail, electrical signals are still provided to the structure through the remaining interconnects.
In one embodiment, the present invention is implemented in an ink-jet print cartridge. The electrical interconnects convey electrical signals through the substrate to printhead structures mounted on the substrate. A conductive layer may be mounted between the substrate and the printhead structures to selectively distribute the electrical signals to the printhead structures. By routing the electrical signals through the substrate, the electrical connections are not exposed to the corrosive effects of the ink ejected from the printhead structures.
The present invention also pertains to a method of forming electrical interconnects through a substrate to structures (devices) mounted on the front side of the substrate. In one embodiment, the method is used to form electrical interconnects for conveying electrical signals through the substrate to ink-jet printhead structures.
In accordance with the present invention, a wet or dry etching process, or another viable process, is used to form a plurality of parallel holes through the substrate. In one embodiment, the holes are formed without reducing the thickness of the substrate.
The holes formed in the substrate in accordance with the present invention have a relatively high aspect ratio (the ratio of their depth to their diameter). In the present embodiment, electric interconnects are formed by coating the sidewalls of the holes in the substrate with a dielectric material and also with a conducting material such that the holes are not completely filled in. Some of the holes may be then filled in with a conducting material. In one embodiment, atomic layer deposition is used to deposit the dielectric material and the conducting material in the holes that are not completely filled in. Electroplating can be used to fill in some of the holes with conducting material. In one embodiment, the electrical interconnect to a structure is formed by electrically coupling the structure to multiple electrical interconnects such that electrical signals to the structure are carried by redundant electrical paths.
In summary, the present invention provides an apparatus incorporating multiple electrical interconnects extending through a substrate, in which a structure is coupled to one or more of the interconnects, and a method of forming the same. As such, it is not necessary to route electrical signals to and along the front surface of the substrate in order to convey the signals to structures mounted on the substrate, simplifying the routing of the signals and reducing the space needed for the routing on the front (top) surface. In an ink-jet printer application, the electrical connections are not exposed to the corrosive effects of ink expelled from printhead structures. These and other objects and advantages of the present invention will become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments that are illustrated in the various drawing figures.